The invention relates to so-called diffused metal oxide semiconductor transistor (DMOST) drivers. Such drivers are disclosed in U.S. Pat. No. 4,888,505, Ser. No. 189,442, which was filed by Timothy J. Skovmand on Mar. 2, 1988. It is titled VOLTAGE MULTIPLIER COMPATIBLE WITH A SELF-ISOLATED C/DMOS PROCESS. A DMOST can drive a load so that the load voltage closely approaches the supply. In order to do this the gate must be overdriven to a significant extent and this necessitates a source of potential that is higher than the operating supply. In this application the boosted potential is achieved by means of a voltage multiplying rectifier driven by the circuit clock. A number of other versions of such "boost" circuits are well known in the art. The above patent issued on Dec. 19, 1989, as U.S. Pat. No. 4,888,505, is assigned to the assignee of the present application and its teaching is incorporated herein by reference.
Such DMOST devices can be constructed to be junction isolated using a complementary semiconductor metal oxide semiconductor (CMOS) process that can also include more conventional bipolar elements normally found in the well-known monolithic silicon planar epitaxial PN junction isolated IC devices. A power DMOST can be created from a large number of small parallel-connected elements. The operating voltage can be kept reasonably high and the current conducting capability can be made substantial. For example, the on resistance of a power DMOST can be made as low as a fraction of an ohm.
Typically, the prior art DMOST IC devices were shut down when the chip temperature exceeds some predetermined threshold. It would be desirable to electronically limit the power dissipation without having to wait for the chip to heat.